tasks a-s

Task/Non-decimal-radices-Convert/Standard-ML/non-decimal-radices-convert.ml

@@ -0,0 +1,25 @@
+fun toBase b v = let
+  fun toBase' (a, 0) = a
+    | toBase' (a, v) = toBase' (v mod b :: a, v div b)
+in
+  toBase' ([], v)
+end
+
+fun fromBase b ds =
+  foldl (fn (k, n) => n * b + k) 0 ds
+
+val toAlphaDigits = let
+  fun convert n = if n < 10 then chr (n + ord #"0")
+                            else chr (n + ord #"a" - 10)
+in
+  implode o map convert
+end
+
+val fromAlphaDigits = let
+  fun convert c = if      Char.isDigit c then ord c - ord #"0"
+                  else if Char.isUpper c then ord c - ord #"A" + 10
+                  else if Char.isLower c then ord c - ord #"a" + 10
+                  else raise Match
+in
+  map convert o explode
+end